1. Field of the Invention
The invention relates to a process for producing thin, anisotropic layers on surface-structured supports.
2. Discussion of the Background
It is known that liquid crystalline substances may be directionally and hence anisotropically oriented by external forces (see Ullmann's Encyclopadie der tech. Chemie, 4th Ed., Vol. 11, pp. 658-671, Verlag Chemie, 1976). Such external forces include electromagnetic fields or mechanical forces, generally shearing or deformation. In addition, surface effects may be utilized, such as those that appear in a uniaxially stretched polyimide (see de Jeu, Physical Properties of Liquid Crystalline Material, Chapter 2, p. 16; J. Cognard, Mol. Cryst. Liq. Cryst. Supplement 1, p. 1 (1982); J. M. Geary, J. W. Goodby, A. R. Kmets, J. S. Patel, J. Appl. Phys., 62, 4100-4108 (1987).
Technically, such liquid crystalline systems are usually used in a sandwich configuration for display applications (see Kelker-Hatz,.Handbook of Liquid Crystals, Chapter 14, p. 611, Verlag Chemie (1980)). With such display cells, macroscopically orientated liquid crystal domains are obtained, such as those used for digital optical display instruments and the like.
Layer thicknesses are between 5-50 microns and are formed by what are known as spacers. The cells are customarily filled by making use of capillary action. In order to produce oriented liquid crystal polymers, the display method has generally been used (see GB-A 2,146,787; GB-A 2,193,338).
The size of the display cells for liquid crystalline polymers is necessarily limited to a maximum of 50.times.50 mm by the viscosity and flow properties of polymers. The filling of the cells in layer thickness of up to 25 microns had to be performed in a vacuum at a high temperatures (T.sub.K +5K). They then had to be tempered to below the clearing temperature (T.sub.K) in order to obtain thorough macroscopic orientation. This process on the one hand involves considerable expenditure of time and subjects the liquid crystal polymers to thermal stress and on the other hand works only for displays of small dimensions.